Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

November 3, 1995

Mr. Paul J. Lawonn
MRA-The Management Association, Inc.
235 North Executive Drive
Suite 100
Brookville, WI 53005-7591

Dear Mr. Lawonn:

This is in response to your September 15 letter requesting an interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHC's) standard, 29 CFR 1910.119. Specifically, you requested clarification as to whether the three processes enclosed with your letter would be covered by the PSM Standard. Your process diagrams are enclosed to facilitate our response.

Process A The use of the hose connection as depicted in the enclosed process A diagram would not preclude this process from being covered by the PSM standard. Delivery of flammable liquid from the atmospheric tank to fill "a portable tank or nearby stationary tank" is considered an onsite movement activity which precedes the handling and use activities of the coating operation. Under the paragraph 1910.119(b) definition of process, the coating operation, including the activities of on-site movement, handling or use, interconnected by way of a hose connection to the flammable liquid atmospheric storage tank is considered a single process. When such a process contains a threshold quantity, that is, 10,000 pounds (9545 kg) or greater amounts of a cover HHC at any one point in time, it is covered by the PSM standard. This interpretation is predicated on the assumption that an event, such as a fire or explosion, will take place notwithstanding engineering (including fusible link check valve) controls and administrative controls required by the PSM standard to prevent a catastrophic release of the HHC.

Process B There is insufficient information on Process B to determine whether this process would be covered by the PSM standard. The process depicted in the Process B diagram would not be covered, under the paragraph 1910.119(a)(1)(ii)(B) exception, when located away from any other HHC process such that there is no reasonable probability that an event such as an explosion in other vessels which contain quantities of the chemical that when added together would exceed the threshold and provide a potential for a catastrophic release. (F.R. 6372)

Process C As explained in the Process A reply above, the use of engineering controls such as those used in the transfer of flammable liquid from the (atmospheric) storage tank to the (atmospheric) process tank as described for Process C would not preclude this process from coverage by the PSM standard.

We appreciate your interest in occupational safety and health. If we can be of further assistance, please contact Ronald J. Davies of my staff at (202) 219-8031, extension 110.


John B. Miles, Jr., Director
Directorate of Compliance Programs


Process A

In this process, solvent is bulk stored in a 3,000 or 5,000 gallon tank. The tank and tank outlet pump are located in a first floor room that contains only solvent storage tanks and their outlet pumps. Piping runs from the tank to a meter mounted on a second floor wall. A hose is screwed into the outlet of the meter. When solvent is needed for a portable tank or a nearby stationary tank, the hose is utilized. On the hose outlet is a gasoline type nozzle. Solvent is metered through the meter outlet hose to the vessel. When metering is complete, the meter hose is returned to its storage position. Fusible link check valves are installed in the tank outlet lines wherever the lines go through a wall and right before the meter.

Enclosure 1

(For Process A, Click Here)


Process B

In this process, solvents and resins are bulk stored and pumped to scale weighing stations. The resin storage tanks range from 1,500 to 5,000 gallons in capacity. The solvent tanks are 3,000 or 5,000 gallons in size. Each solvent or resin tank has its own outlet pump located next to it. The pumps are activated by a switch located next the manual ball valve at the outlet pipe end. When resin or solvent is needed, a portable tank is rolled onto the scale. Directly over the scale are the solvent and resin outlet pipes. The ball valve is manually opened, the switch manually activated and material flows into the tank until the desired weight is reached. Then the switch is manually deactivated, the ball valve is manually closed and the tank is rolled away.

Fusible link check valves are installed in the solvent tank outlet lines wherever the lines go through the wall. A fusible link check valve is installed in each resin tank outlet line at the resin tank. Both solvent and resin outlet pipes at the scale have fusible link check valves installed in them. They are directly above the floor scale.

Enclosure 2

(For Process B, Click Here)


Process C

In this process, resin is stored in a 7,500 gallon storage tank on load cells. The outlet pump is located next to the storage tank; outlet piping is run to a 2,500 gallon process tank that hangs through the second floor. The piping from the resin storage tank is permanently connected to the 2,500 gallon process tank. There is an actuated ball valve in the piping at the process tank. When material is needed, the resin weight is entered into a control panel and a start button is pushed. The actuated ball valve opens and resin is pumped in to the process tank until the desired weight is reached. The ball valve then closes and the pump stops.

Enclosure 3

(For Process C, Click Here)